Vertical distribution of aggregates (>110 µm) and mesoscale activity in the northeastern Atlantic: Effects on the deep vertical export of surface carbon

Abstract

Spatial and temporal variability in the distribution of marine aggregates (.110 mm) was studied using underwater video profilers in an area off the Iberian Peninsula and Azores Islands dominated by mesoscale and submesocale hydrodynamics in winter, spring, and summer 2001. In the 0-200-m layer, aggregates were most abundant in spring (100-120 mg dry weight [dry wt] m 23 ) and lowest during summer and winter (1-10 mg dry wt m 23 ). In the deeper layers (down to 1,000 m), the seasonal pattern was different, with concentrations highest in spring and summer, and lowest in winter (e.g., at 800 m, 5-10 mg dry wt m 23 in spring and summer; 1-5 mg dry wt m 23 in winter). The seasonal change in the abundance of aggregates in the upper 1,000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps and with seasonal changes in the surface phytoplankton community. In an area dominated by eddies, surface accumulation of aggregates and export down to 1,000 m occur at mesoscale distances (,100 km). The occurrence of a rich aggregate layer may be related to mesoscale activity in water flow that drives nutrient inputs, phytoplankton production, and the formation of large aggregates. Such spatially constrained zones of massive export may be typical of frontal open-sea systems, and may have been missed by conventional sediment trap moorings, which cannot resolve export at this mesoscale level.

The Underwater Vision Profiler 5: An advanced instrument for high spatial resolution studies of particle size spectra and zooplankton

“…These assemblages were consistent with epipelagic biogeochemical provinces (Longhurst 1995). In another experiment, the combinations of the 2 systems (UVP2 and UVP4) documented that mesoscale Atlantic eddies spatially constrain the export of particles in different seasons (Guidi et al 2007). More recently, an analysis of the complete database generated by these instruments shows that the particle size distribution in the mesopelagic layer is closely related to the size distribution of the phytoplankton in the euphotic zone (Guidi et al 2009).…”

“…Using sediment trap data, Guidi et al (2008) showed that particle size distribution can also be used to estimate the potential particle settling speed, and hence, mass fluxes in the water column at global scale. This proxy of particle flux serves to detail the vertical resolution of fluxes and estimates the particle remineralization rate that is used in biogeochemical modeling to describe the decrease of the export with depth (Guidi et al 2009).…”

“…This proxy of particle flux serves to detail the vertical resolution of fluxes and estimates the particle remineralization rate that is used in biogeochemical modeling to describe the decrease of the export with depth (Guidi et al 2009). The UVP5 provides information on particle size distribution at high spatial resolution allowing the description of spatial distribution of carbon flux in different hydrological regimes, frontal zones, gyres, and equatorial systems (Gorsky et al 2002;Gorsky et al 2003Guidi et al 2007Stemmann et al 2008b). The completion of work at high spatial resolution revealed that particle distributions can be constrained in space-inducing heterogeneous export in the open ocean.…”

“…The original UVP and its successor instruments, versions 2 through 4, were large stand-alone packages of nearly 1 m 3 and incorporated a CTD fluorometer and nephelometer (Gorsky et al 1992;Gorsky et al 2000). UVP2 and 4 have both been used extensively and have been intercalibrated (Guidi et al 2007(Guidi et al , 2009. UVP4 continues to be used for the assessment of a global distribution of mesopelagic macrozooplankton (Stemmann et al 2008c).…”

Role of macroscopic particles in deep-sea oxygen consumption

“…Using both techniques in tandem, we can contrast the relative distribution of microscopic and macroscopic particles in the ocean. Most video profiles in the past have been taken to a maximum depth of 1,500 m (8)(9)(10), and very few profiles exist to 4,000 m (11,12). Thus, the data presented here, with a maximum deployment depth of 6,000 m, represent the most comprehensive basin-scale video analyses of deep-sea particles to date.…”